Conventionally, a developing device detachably attached to an electro-photographic type printer is known. The developing device includes a frame, a developing roller supported to the frame and carrying toner thereon, a thickness regulation blade for regulating a thickness of a toner layer carried on the developing roller, and a seal member preventing toner from leaking from the frame.
The developing device is provided with a developer cartridge having the thickness regulation blade and the seal member. The thickness regulation blade includes a leaf spring member having generally rectangular shape in front view and a pressing portion provided at a free end portion of the leaf spring member and in contact with the developing roller. The seal member is provided with a blade side seal disposed between each widthwise end portion of the leaf spring member and each axial end portion of the developing roller. The seal member is also provided with a side seal at the widthwise end portion of the frame. The side seal is in frictional contact with the outer peripheral surface of the developing roller.
According to this developer cartridge, one end portion of the side seal is positioned to cover the blade side seal, and the blade side seal prevents the toner from leaking through a boundary between the widthwise end portion of the leaf spring and the axial end portion of the developing roller. Further, the side seal prevents the toner from leaking through a boundary between the widthwise end portion of the frame and the outer peripheral surface of the developing roller.